Trouble connecting an Inspiron 6000 laptop to a 2400MP projector

I am trying to set up a Dell 2400MP projector to an Inspiron 6000 laptop via a vga connection. The projector is in a church and is ceiling mounted, so we have a box to boost the signal. (not sure of the technical term for the box) but it connects diretly into the VGA port on the back of the laptop. The problem is being able to use the toggle function to have both laptop and screen running at the same time. We have another laptop that's exactly the same, except that it has a higher res screen. It works fine. I've checked the settings on both and they have the same graphics card, a Mobile Intel(R) 915 GM/GMS. 910 GML Express Chipset. Any thoughts on the problem? :smileyindifferent: